Iterative atrial tachycardia originating from the coronary sinus musculature.

A case of iterative atrial tachycardia leading to dilated cardiomyopathy is reported. During electrophysiologic study, the tachycardia showed a markedly irregular cycle length associated with changes in atrial activation breakthrough as demonstrated by coronary sinus (CS) recordings and frequently degenerated into self-terminating atrial fibrillation. Left atrial transseptal mapping demonstrated the earliest endocardial atrial activation close to the posterolateral mitral annulus, but this was invariably later than that recorded within the CS, where low-energy radiofrequency applications eliminated the tachycardia. No acute vessel damage was observed at postablation CS angiography. In accordance with previously published experimental data, we hypothesized that the muscular sleeves surrounding the CS might be involved in the genesis of this tachycardia. During 6-month follow-up, the patient remained asymptomatic without tachycardia recurrences and with complete recovery of left ventricular function, confirming the reversible nature of the tachycardia-induced cardiomyopathy.